An anisotropic conductive member, when inserted between an electronic component such as a semiconductor device and a circuit board, then subjected to merely the application of pressure, is able to provide an electrical connection between the electronic component and the circuit board. Accordingly, such members are highly attractive members that are widely used, for example, as connecting members for semiconductor devices and other electronic components and as inspection connectors when carrying out functional inspections, and that can be expected to be applied to optical transmission materials.
In particular, owing to the remarkable degree of miniaturization that has occurred in electronically connecting members for semiconductor devices and the like, connection stability cannot be fully guaranteed in conventional techniques such as wire bonding that involve the direct connection of a wiring substrate. This situation has drawn attention in recent years to anisotropic conductive members of a type in which an array of electrically conductive elements pass completely through a film of insulating material, or of a type in which metal balls are arranged in a film of insulating material.
Inspection connectors have been developed to avoid the large monetary losses that are incurred when, upon carrying out functional inspections after an electronic component such as a semiconductor device has been mounted on a circuit board, the electronic component is found to be defective and the circuit board is discarded together with the electronic component. By bringing electronic components such as semiconductor devices into electrical contact with a circuit board through an anisotropic conductive member at positions similar to those to be used during mounting and carrying out functional inspections, it is possible to perform the functional inspections without mounting the electronic components on the circuit board, thus enabling the above problem to be avoided.
An anisotropic conductive member used in such applications is described in Patent Document 1, which discloses “an anisotropic conductive film comprising a film substrate composed of an adhesive insulating material and a plurality of conductive paths composed of a conductive material which are arrayed within the film substrate in a mutually insulated state and pass entirely through the film substrate in a thickness direction thereof, wherein the conductive paths have shapes, in a cross-section parallel to a lengthwise direction of the film substrate, with circumferences having thereon an average maximum length between two points of from 10 to 30 μm, and wherein neighboring conductive paths have intervals therebetween which are from 0.5 to 3 times the average maximum length.”
Patent Document 2 discloses “an anisotropic conductive film comprising a film base composed of an insulating resin and a plurality of conductive paths which are mutually insulated, pass entirely through the film base in a thickness direction thereof and are positioned in staggered rows, wherein conductive paths in mutually neighboring conductive path rows have a smaller distance therebetween than conductive paths within a single row of conductive paths.”
Patent Documents 1 and 2 disclose methods of manufacturing such anisotropic conductive films in which fine wires of an anisotropic conductive material are inserted into an insulating film, the elements are integrally united by the application of heat and pressure, and scribing is subsequently carried out in the thickness direction.
Patent Document 3 examines a method of manufacturing an anisotropic conductive film which involves electroforming conductive columns using a resist and a mask, then pouring an insulating material in the columns and solidifying the insulating material.
Patent Document 4 discloses “a method of manufacturing an electrically connecting member having a retaining body made of an electrically insulating material and a plurality of conductive elements provided in a mutually insulating state within the retaining body, wherein an end of each conductive element is exposed on a side of the retaining body and the other end of each conductive element is exposed on the other side of the retaining body, the method comprising:
a first step of exposing a matrix having a base and an insulating layer which, when deposited on the base, forms the retaining body to a high energy beam from the insulating layer side, thereby removing all of the insulating layer and part of the base in a plurality of regions so as to form a plurality of holes in the matrix;
a second step of filling the plurality of formed holes with a conductive material for forming the conductive elements so as to be flush with the sides of the insulating layer or to protrude from the sides; and a third step of removing the base.” Patent Document 4 also carries out investigations on various materials (e.g., polyimide resins, epoxy resins and silicone resins) for the insulating layer.
However, with the increasing trend in recent years toward higher integration, electrode (terminal) sizes in electronic components such as semiconductor devices are becoming smaller, the number of electrodes (terminals) is increasing, and the distance between terminals is becoming smaller. Moreover, there have also appeared electronic components having a surface construction wherein the surface on each of the numerous terminals arranged at a narrow pitch lies at a position that is more recessed than the surface of the component itself.
In order to be able to adapt to such electronic components, there has arisen a need to make the outer diameter (thickness) of the conductive paths in anisotropic conductive members smaller and to arrange the conductive paths at a narrower pitch.
However, in the methods of manufacturing the anisotropic conductive films and electrically connecting members described in Patent Documents 1 to 4, it has been very difficult to reduce the size of the conductive paths. A method of filling the conductive material suitable to the narrow pitch at a high density is expected.    Patent Document 1: JP 2000-012619 A;    Patent Document 2: JP 2005-085634 A;    Patent Document 3: JP 2002-134570 A;    Patent Document 4: JP 03-182081 A;